# Chains under fire trucks **URL:** \ **Category:** Factual Questions\ **Created:** [May 25, 2006, 5:54pm UTC](https://boards.straightdope.com/t/chains-under-fire-trucks/358206 "2006-05-25T17:54:53Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![Jombi](https://avatars.discourse-cdn.com/v4/letter/j/f19dbf/32.png) [@Jombi](https://boards.straightdope.com/u/Jombi)\ **Post date:** [May 25, 2006, 5:54pm UTC](https://boards.straightdope.com/t/chains-under-fire-trucks/358206/1 "2006-05-25T17:54:53Z")
What are those chains I see dangling from the rear axle of a fire truck? They’re not snow chains. (We don’t get snow, and they’re right in the middle of the axle, nowhere near the tires.) They seem to dangle just short of touching the road. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [May 25, 2006, 6:02pm UTC](https://boards.straightdope.com/t/chains-under-fire-trucks/358206/2 "2006-05-25T18:02:15Z")
I would guess static electricity suppressors/dispersers. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [May 25, 2006, 6:02pm UTC](https://boards.straightdope.com/t/chains-under-fire-trucks/358206/3 "2006-05-25T18:02:32Z")
The chains are meant to dissipate static electricity buildup, by giving it a safe path to ground. Unintended static sparks around gasoline and other fuel vapors is a Bad Thing, particularly when you’re there to PUT OUT a fire, not start one. ---
**Author:** ![Sunspace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunspace/32/1250_2.png) [@Sunspace](https://boards.straightdope.com/u/Sunspace)\ **Post date:** [May 25, 2006, 6:26pm UTC](https://boards.straightdope.com/t/chains-under-fire-trucks/358206/4 "2006-05-25T18:26:48Z")
Are these the same things that I sometimes see hanging down to the road surface beneath the rear bumpers of cars: loosely-hinged sticks with a triangular symbol on them? ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [May 25, 2006, 6:31pm UTC](https://boards.straightdope.com/t/chains-under-fire-trucks/358206/5 "2006-05-25T18:31:54Z")
They might be part of a chain on the fly system. When engaged the chains rotate at the axle speed and thoses hanging chains now fan out in a way that the chain will go under the drive wheel, which is driven over for traction. Not only for snow/ice but also for other limited traction surfaces like dirt/mud. ---
**Author:** ![enipla](https://avatars.discourse-cdn.com/v4/letter/e/54ee81/32.png) [@enipla](https://boards.straightdope.com/u/enipla)\ **Post date:** [May 25, 2006, 6:39pm UTC](https://boards.straightdope.com/t/chains-under-fire-trucks/358206/6 "2006-05-25T18:39:39Z")
> [@kanicbird](#): > > They might be part of a chain on the fly system. When engaged the chains rotate at the axle speed and thoses hanging chains now fan out in a way that the chain will go under the drive wheel, which is driven over for traction. > > Not only for snow/ice but also for other limited traction surfaces like dirt/mud. Sounds like what the OP is describing. Lots of vehicles have these where I live [automatic tire chains](http://www.insta-chain.com/) ---
**Author:** ![Jombi](https://avatars.discourse-cdn.com/v4/letter/j/f19dbf/32.png) [@Jombi](https://boards.straightdope.com/u/Jombi)\ **Post date:** [May 25, 2006, 6:50pm UTC](https://boards.straightdope.com/t/chains-under-fire-trucks/358206/7 "2006-05-25T18:50:31Z")
Not the chain on the fly system. Nowhere near that close to the wheels and not that much chain or apparatus either. Just a few chains hanging down near the round bulge on teh axle (whatever that is, obviously I’m not mechanically inclined). Soudns to me like the static suppressor is the likely answer for what I’m seeing. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [May 25, 2006, 7:55pm UTC](https://boards.straightdope.com/t/chains-under-fire-trucks/358206/8 "2006-05-25T19:55:17Z")
> [@Jombi](#): > > Not the chain on the fly system. Nowhere near that close to the wheels and not that much chain or apparatus either. Well if you look at the link above you would see that the chain on the fly systems store near the center diff and hang down just as you describe it. Also the system linked to have as few as 6 chains, 1/2 of which would be attached to the ‘top’ of the disk and may not be visable.